Studies of calcium emission stars. I. HD 158393, a giant star in a binary system.
Lloyd Evans, T.; Balona, L. A.; Fekel, Francis C.
South Africa, United States
Abstract
HD 158393 is a giant star of spectral type late G or early K which has moderately strong Ca II H and K emission cores. UBVRIJHK photometry and IUE spectra reveal a companion of type F0 - F2, luminosity class IV or V. Radial velocity data yield an orbit with a period of 31 day. The K and F stars have nearly equal mass, with a minimum value of 1.7 M_sun;. The strong Ca II emission indicates an enhanced chromospheric activity which is typical of giant stars in a binary system of this period, and the light is variable in a 31-day period indicative of synchronous rotation as well as on a long time-scale. Analysis of the 31-day light period by fitting a spot model indicates the presence of two spots in 1975 and 1976. The two spots showed different periods and were at different latitudes, suggesting differential rotation of the giant star.